1. Technical Field of the Invention
This invention most generally relates to the alignment of planar arrays of electro-optical devices with optical link connectors used for multi-channel optical data communications; and more particularly to a method for mapping the result of a non-critical physical alignment of an optical array to a multi-channel optical link connector where multiple electro-optical devices are available for each optical channel.
2. Background Art
Integrated circuit technology allows large numbers of VCSEL (Vertical Cavity Surface Emitting Laser) laser emitter optical transmitters and p-i-n diode photo detector optical receivers to be constructed as large, two dimensional planar arrays, with one or more such arrays mounted on a common ASIC (Application Specific Integrated Circuit) substrate, as by flip-chip methods, also known as hybridization mounting techniques, each emitter and/or detector of the array making electrical connections with circuitry previously constructed in the ASIC substrate. This compound device, when coupled with precision alignment to a terminal end or node of a multi-channel optical link such as the end of a fiber optic bundle, provides an electro/optical communications interface where an electronic signal is converted by a VCSEL to an optical signal, directed at a end face of a single channel optical core of a terminator/connector, and hence along an optical transmission path fiber within the bundle, to be discharged via a carefully aligned receiving end fiber terminator/connector into a photo diode opto-electronic receiver on the same or another optical array of the same or another ASIC substrate, and converted by that photo detector back into an electronic signal. Fiberoptic communications channels provide significantly greater speed and effective bandwidth capabilities as compared to electrically conductive leads.
Each core end of the optical fiber bundle terminator or connector must be carefully aligned with its VCSEL on one end and corresponding detector on the end in order for the optical communications channel to be effective. Light pipes and image guides are commonly used to terminate a fiber bundle and connect the individual light fibers to their respective optical elements in planar photo arrays. These must be carefully aligned without actual contact and mechanically fastened to the planar array or its ASIC substrate so as to maintain optical alignment. Sufficient misalignment between the optical face of the array and the terminator face, in any of the Z-axis parameters of lateral offset, rotation, tilt, and spacing as between a multi-channel fiber terminator and a photo optic array, can cause a significant number of optical channels to be unusable.
As the density of the arrays of emitters and detectors increases, coupling a multi-channel fiber optic cable, image guide, or other optical connector or terminating device to the transceiver array becomes an increasingly more arduous task. Lateral offset and rotation alignment are particularly burdensome, while spacing and tilt alignment are more easily controlled with proper mechanical connectors and spacing structures.
Two intuitive methods for aligning an optical fiber array to its respective electro-optical array to achieve accurate device-to-channel alignment, should be noted. The fabricator may simply observe the electro-optical devices through a part of the connector and visually or xe2x80x9cpassivelyxe2x80x9d align target reference points of the components, perhaps with the aid of a transparent fiber alignment faceplate or template. Another method is to interconnect all of the various electrical and optical assemblies and perform xe2x80x9cactivexe2x80x9d final physical alignment of the multi-channel fiber connector to the optical array so as to optimize the multi-channel connection as seen at the detector side of the optical link, and then secure the connector to the optical array or its ASIC substrate in that precise position. In either event, each such connection requires a closely controlled, precise step in the assembly process that contributes to the time and cost to assemble devices employing this technology.
It is an objective of the invention to provide a method for determining the alignment of a multi-channel optical link connector to a planar optical array.
It is another objective of the invention to provide a method for determining the alignment of each of the channels of a multi-channel optical link connector to the optical devices on a planar optical array.
It is a further objective to provide a method for determining the alignment of both ends of each of the channels of a multi-channel optical link to the optical devices of respective planar optical arrays.
For proper performance of electro-optical planar array devices used to provide data communications over optical links, it is essential that there is sufficient control over the alignment of the optical array face with respect to the optical link connector to assure an effective optical communications channel is present between identifiable sets of emitters and detectors. This invention desensitizes the precision required of the physical alignment of a multi-channel fiber optic link connector to the optical planar array face as compared to the one to one correspondence between an optical fiber termination and an optical device as used in the prior art.
The invention depends on using undersampling techniques that assume each fiber will be optically connected to several emitters on one end and/or several detectors on the other end, in combination with an automated mapping of the physical alignment of a non-precision connection which sorts out the available channels of the optical link and the emitter sets and detector sets common to each channel. This self-determination methodology of alignment provides data that then permits selection and de-selection from among the individual emitters and detectors on each array in accordance with various schemes for optimizing the performance of each channel of the communications link.
VCSELs can be produced in planar arrays by several methods. Ion-implanted VCSELs can be made with a diameter ranging from 20 to 100 microns. Oxide VCSELs can range from 20 to 60 microns. Etched-post VSCEL arrays are now feasible with VCSEL diameters of 5 to 40 microns; and with a 2 micron wide trench, can have a pitch as small as about 7 microns. This provides the potential for a significant planar face density of optical devices per fiber channel, using, for example, 50 or 62.5 micron diameter fiber cores terminated in a suitable connector.
Summarizing the technique of the invention for the simpler case, during the self-alignment of an under-sampled transmitter array to the fiber bundle, the transmitters devices are activated, for example in a rastering mode, while the detector array receiving the time-related impulses, and its controlling software embedded in the underlying ASIC or in the ASIC in combination with remote circuitry and software, map the unique set of adjacent transmitters producing a respond in each detector. If the detector array is connected on a one to one basis with the fibers or optical channels of the optical link, then the emitter set for that channel has been identified, in effect establishing the result of the physical alignment and mounting of the fiber optic connector to the transmitter array.
The use of multiple emitters per channel, along with the self-determined alignment information, provides further opportunities for individual selection, de-selection and control of the emitters within the set to optimize the use of each channel. As will be readily apparent to those skilled in the art, the corresponding methodology and the further opportunity for the case of an under-sampled receiver array is quite similar, except that detector sets for each emitter channel are identified, and subsequent control of detectors can be exercised for optimizing channel performance.
In the simplest case, for determining which detectors have been excluded from all possible channels by the particular physical connection of a multi-channel optical link to a detector array, as made during fabrication, the all-channels to all detectors alignment can be accomplished by simply illuminating the other, input end of the optical link with an expanded beam of suitable wavelength so that detectors adequately coupled to any channel will respond and be recognized.
A logical further scenario is where there are multiple optical devices at each end of each fiber channel. They may, of course, be on the same optical chip, on different optical chips on the same ASIC substrate, or on optical chips on different ASIC substrates. The invention also extends to chips of any sort that may integrate the ASIC and electro-optical surface arrays for both intra-chip and inter-chip optical communication, where assembly requires physical alignment of a multi-channel optical link connector to at least one planar array of optical devices on the chip, or as in this case, with both ends of the multi-channel link connected each to a planar array of optical devices.
In this case, the automatic self-determination alignment methodology of the invention requires the following steps:
1. Interconnect two planar arrays of very small electro-optical devices of photo-emitters and detectors with a multi-channel fiberoptic bundle, or optical link, where each end of the bundle is terminated by a suitable connector, each of which is attached to one of the arrays, so that each fiber of the bundle is linked to or xe2x80x9cseesxe2x80x9d at one end several electro-optical emitters on one array and is linked to or xe2x80x9cseesxe2x80x9d at its other end several electro-optical detectors on the other array. The interconnect step in this case is a relatively non-precise physical operation with respect to lateral offset and rotation, but is still sufficiently precise to assure proper Z-axis spacing and tilt tolerances of the optical link connectors to the optical arrays. It does not depend on critical alignment of channels to respective optical devices, but rather on overall array to connector edge alignment, since it is not necessary to establish an exact alignment or to achieve a pre-determined optical device-to-channel alignment at this stage.
2. Enable all of the detectors on the receiver array, or on both arrays or each array in turn if using transceiver arrays. This is done through ASIC or ASIC in combination with remote control circuitry and software.
3. Raster or otherwise sequence the individual photo emitters of the transmitter array, or on both arrays or each array in turn if using transceiver arrays. This is likewise done through ASIC or ASIC in combination with remote control circuitry and software.
4. Record the particular detectors illuminated with respect to each emitter in turn. When an emitter device of the transmitting array is on, only those detectors that are aligned with the same optical fiber serving that emitter will have useful sensitivity. Blanket illumination of the detector arrays is prevented because of the occulting portions of the optical fiber array. The effect is the same for an ordered fiber bundle or a more common over-sampling image guide. The ability to monitor and record or xe2x80x9cmapxe2x80x9d the detector response is resident within the local ASIC, or is shared with remote control circuitry and software.
5. Establish, again through the ASIC or in combination with remote control circuitry and software, the detector sets of adjacent detectors common to each emitter as seen through the optical link.
6. Match up common sets of detectors to identify emitter sets of adjacent emitters using a common optical channel, again through the ASIC or in combination with remote control circuitry and software.
The methodology may be extended to mapping and recording the intensity or signal strength of each emitter/detector pair within a given optical channel, so that there may be a suitable initial selection from among the emitters and detectors of associated emitter and detector sets using the same channel that optimizes that channel of the communication link. The channel""s emitter/detector pairs intensity map can be periodically compared to a fresh mapping of channel intensity, for possible re-selection of suitable emitters and detectors from amount those available.
A further benefit of the undersampling and mapping scheme is that spare emitters and detectors within the channel are available, should there be a failure of one of these optical devices. The methodology supports the implementation of differential optical signals in a given channel, using selective combinations of available emitters and detectors from among the emitter and detector sets of the channel.
On a larger scale, the methodology of the invention provides for periodic or automatic alignment assessments of the connector to the optical planar array to guard against creeping physical re-alignment due to environmental effects such as deforming temperature, torque or pressure on the device. When necessary, the full, self-alignment mapping procedure can be run again to reset the baseline emitter and detector sets for each channel.
It will be readily apparent that fiber channels with multiple optical devices at each end, such as where being connected to transceiver arrays with uniformly distributed emitters and detectors, may have bi-directional capability for all or some channels. The fully defined physical alignment map provides the data necessary for selection, de-selection and control of the devices at each end of the link, enabling ASIC and remote control circuitry and software to manipulate both direction and performance of each channel, within the total capability of the devices associated with that channel.
It will be further apparent to those skilled in the art that the methodology can be extended to compound optical links having more than two connectors or nodes, where transmitters from one array may be linked with and communicating to detectors of two or more other arrays, or where detectors in one array may be linked to receive data from either of two or more transmitter arrays, or as may otherwise be required in variations of simplex, duplex, star and ring interconnect topologies.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein we have shown and described only a preferred embodiment of the invention, simply by way of illustration of the best mode contemplated by us on carrying out our invention.